Proton-impact-induced electron emission from biologically relevant molecules studied with a screened independent atom model

We use the recently introduced independent-atom-model pixel counting method to calculate proton-impact net ionization cross sections for a large class of biologically relevant systems including pyrimidines, purines, amino acids, and nucleotides from 10 keV to 10 MeV impact energy. Overall good agreement with experimental data, where available, is found. A scaling prescription that involves coefficients derived from the independent atom model is shown to represent the cross section results better than scalings based on the number of (bonding) valence electrons of the target molecules. It is shown that the scaled net ionization cross sections of the proton-nucleotide collision systems can be represented in terms of a simple analytical formula with four parameters to within 3% accuracy.